"We were forced to react. Excuse me, but those are the rules ... and our Nato colleagues, at least those who initiated the expulsion of our diplomats, couldn't have expected anything less from us," he said.

Nato 'unpredictable'

Dmitry Rogozin, Russia's ambassador to Nato, was highly critical of the military alliance in an interview with Russian newspaper Izvestia.

"This organisation is becoming more and more unpredictable ... The alliance can't seem to behave in a respectable, stable and decent way," he said.

Nato, which invited many non-member countries to take part in the games, has said the exercises pose no threat to Russia.

They are being seen as a gesture of solidarity with Georgia, which aims to become a member of the military alliance - a move also opposed by Russia.